<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>JS基本语法</title>
    </head>
    <body>
        <script>
            var x;
            let y = 5;
            const PI = 3.14;
            console.log(x,y,PI);
            let name = "如花";
            console.log(name);
            let empty_value = null;
            console.log(empty_value);

            let age = 17;
            if(age >= 18){
                console.log("成年了");
            }else{
                console.log("未成年");
            }
            
        </script>
    </body>
</html>